Coolant Temp Increasing at Highway Speeds

[Bowhunter]

I found this post from a member back in 2020. I don’t know the age of my cooking parts (other than the redish coolant is somewhat new) but what he explains is am exactly what I’m experiencing. For my next try, I’m debating between trying to drain all the redish coolant out and put new GO5 or replace fan clutch


I've been closely following threads like this. I've never been happy with the fact that when the outside temp was above 60° F and at sustained highway speeds, my needle would move to the right edge of the zero in the 210 label on the gauge.

The radiator, hoses, water pump, thermostat, and radiator cap were all replaced new when a new long block was installed two years ago. Temperatures were not erratic, indicating neither a bad sensor nor air in the system. I'm running a Stant 18lb radiator cap, but swapping caps made no difference. Coolant is fresh and of the proper type and 50/50 mix. Coolant level was stable in the bottle with no boiling or gurgling when hot. The only thing that wasn't new was the fan clutch. When I would slow down, the needle would fall down to the center mark, so I assumed the fan clutch was working as it should. It wasn't overheating, just running hotter than maybe it should.

However, the repeated statements by many here that a properly functioning system should keep the needle close to the center mark bugged me, so I bought an OBDII reader and downloaded the Torque OBD app and started monitoring.

In checking the dash gauge to the reality of what the sensor was reporting through the OBD, what I found was that the temperature range indicated by the my dash gauge is about 195° F when the needle is on the left edge of the "2" and was at about 230° F when the needle was at the right edge of the "0". Needle dead center is 212° F.

Then I kept reading @Jerry Bransford posts where he recommends trying to spin the fan when the engine is hot (but not running!) OK, I could move it pretty easily, but it didn't "spin." So I checked it with the engine cold and found about the same resistance to movement. Concluding that this probably just wasn't right, I bought a new fan clutch and spent 45 minutes changing it.

What a difference.

The temp gauge needle now rarely moves above dead center unless I'm hauling it down the highway in really hot temps. I went off-roading the day I changed the fan clutch and the needle never even got to center point even though it was all slow-crawling and idling in 102° F heat

 

[lBasket]

I found this post from a member back in 2020. I don’t know the age of my cooking parts (other than the redish coolant is somewhat new) but what he explains is am exactly what I’m experiencing. For my next try, I’m debating between trying to drain all the redish coolant out and put new GO5 or replace fan clutch


I've been closely following threads like this. I've never been happy with the fact that when the outside temp was above 60° F and at sustained highway speeds, my needle would move to the right edge of the zero in the 210 label on the gauge.

The radiator, hoses, water pump, thermostat, and radiator cap were all replaced new when a new long block was installed two years ago. Temperatures were not erratic, indicating neither a bad sensor nor air in the system. I'm running a Stant 18lb radiator cap, but swapping caps made no difference. Coolant is fresh and of the proper type and 50/50 mix. Coolant level was stable in the bottle with no boiling or gurgling when hot. The only thing that wasn't new was the fan clutch. When I would slow down, the needle would fall down to the center mark, so I assumed the fan clutch was working as it should. It wasn't overheating, just running hotter than maybe it should.

However, the repeated statements by many here that a properly functioning system should keep the needle close to the center mark bugged me, so I bought an OBDII reader and downloaded the Torque OBD app and started monitoring.

In checking the dash gauge to the reality of what the sensor was reporting through the OBD, what I found was that the temperature range indicated by the my dash gauge is about 195° F when the needle is on the left edge of the "2" and was at about 230° F when the needle was at the right edge of the "0". Needle dead center is 212° F.

Then I kept reading @Jerry Bransford posts where he recommends trying to spin the fan when the engine is hot (but not running!) OK, I could move it pretty easily, but it didn't "spin." So I checked it with the engine cold and found about the same resistance to movement. Concluding that this probably just wasn't right, I bought a new fan clutch and spent 45 minutes changing it.

What a difference.

The temp gauge needle now rarely moves above dead center unless I'm hauling it down the highway in really hot temps. I went off-roading the day I changed the fan clutch and the needle never even got to center point even though it was all slow-crawling and idling in 102° F heat

It seems odd that a bad fan clutch would cause overheating at highway speeds, and not when stopped, doesn't it?

 

[Bowhunter]

It seems odd that a bad fan clutch would cause overheating at highway speeds, and not when stopped, doesn't it?

It does but I went on to read that this member thinks he caught a fan clutch on its way out. Since it hasn’t failed entirely the low speed coolant temp wasn’t having issues yet. (Referencing post 43 till the end
https://wranglertjforum.com/threads/what-temperature-does-your-jeep-run-at.38652/page-3The)

I’m also thinking if there’s not enough resistance when it’s warm, the blades on the fan reduce the amount of air flow that can be pushed through the radiator because they are spinning and slowing the hwy speed air down

resistance in my fan clutch when hot and cold is the same from what I can tell. The fan clutch doesn’t spin much at all, when I apply a decent amount of force trying to spin it, it will travel to about the next blade from where I let it go when trying to spin it

 

[lBasket]

It does but I went on to read that this member thinks he caught a fan clutch on its way out. Since it hasn’t failed entirely the low speed coolant temp wasn’t having issues yet. (Referencing post 43 till the end
https://wranglertjforum.com/threads/what-temperature-does-your-jeep-run-at.38652/page-3The)

I’m also thinking if there’s not enough resistance when it’s warm, the blades on the fan reduce the amount of air flow that can be pushed through the radiator because they are spinning and slowing the hwy speed air down

resistance in my fan clutch when hot and cold is the same from what I can tell. The fan clutch doesn’t spin much at all, when I apply a decent amount of force trying to spin it, it will travel to about the next blade from where I let it go when trying to spin it

What is the failure mode of the clutch? Is it to let go? I thought it was to freeze up.

If you're not overheating at idle, the fan has got to be working, at least partially, I'd think.

For what it's worth, when I messed with my fan over the weekend while I was addressing some temp issues I couldn't honestly tell the difference between cold and warm. Could just be me though

 

[Bowhunter]

What is the failure mode of the clutch? Is it to let go? I thought it was to freeze up.

If you're not overheating at idle, the fan has got to be working, at least partially, I'd think.

For what it's worth, when I messed with my fan over the weekend while I was addressing some temp issues I couldn't honestly tell the difference between cold and warm. Could just be me though

I was of the same thought until I read that post #43.

I’ll put that on the back burning for a minute. What’s the next thing you’d try/change in my current situation?

By the way I appreciate your help and all that post on this topic!

 

[lBasket]

I was of the same thought until I read that post #43.

I’ll put that on the back burning for a minute. What’s the next thing you’d try/change in my current situation?

By the way I appreciate your help and all that post on this topic!

You're sure you're not diluting pre-diluted coolant?

I thought the proper coolant for these was green but not sure that could be related.

I'm not entirely sure at the moment, just thinking outloud I guess. You're having the exact opposite problem I was having - I was overheating at idle, and not when driving. But it ended up being my tstat sticking shut.

The fact that your problem is when on the highway - more air flow (probably not fan?) but more heat generated sounds like something isn't working at the right efficiency.

If you needed to bleed the system, wouldn't the temp fluctuate as air went through the block? I'm not sure on that, seems logical

 

[Bowhunter]

You're sure you're not diluting pre-diluted coolant?

I thought the proper coolant for these was green but not sure that could be related.

I'm not entirely sure at the moment, just thinking outloud I guess. You're having the exact opposite problem I was having - I was overheating at idle, and not when driving. But it ended up being my tstat sticking shut.

The fact that your problem is when on the highway - more air flow (probably not fan?) but more heat generated sounds like something isn't working at the right efficiency.

If you needed to bleed the system, wouldn't the temp fluctuate as air went through the block? I'm not sure on that, seems logical

I agree, I think I would be seeing rapid temp fluctuations if there was air in the system (since I’ve had discovered this hwy temp issue, rapid temp changes hasn’t been an issue on the OBD reader)

I originally decided to dilute my redish (not rust) coolant from the PO because when I tested it using my Preston’s gauge, the arrow was pointed all the way off (off the scale, well above the 268 degree boiling temp mark). I’ve been pulling the straight coolant out and mixing it 50/50 with distilled until I got to this point yesterday which I believe should be close to 50/50 in the whole cooling system. Attached picture is the 50/50 mix I’ve been putting into the radiator. When I tested the radiator last night after the last addition of 50/50 and 25 mile hwy drive, I was at the 268 boil mark on the gauge

I’m tempted to go drain all this red coolant, and replace it with the GO5 everyone on here recommends. Hopefully if I don’t get it all out it doesn’t gell up by mixing the two (some posts about that on this forum) Then if it’s not that, maybe the fan clutch?

 

[Mac57]

So, right now you are running an unknown type of red colored coolant and you have been diluting it with water as well. That's a problem. Next step should be to do the coolant system chemical flush right now. Then fully drain the system with the mystery red coolant and refill with the proper HOAT coolant. Burp as necessary. See if that solves your overheating problem. If not at least you know the system is clean and has the right coolant in it, you can then move on to looking at possible other causes such as a failed fan clutch.

 

[lBasket]

So, right now you are running an unknown type of red colored coolant and you have been diluting it with water as well. That's a problem. Next step should be to do the coolant system chemical flush right now. Then fully drain the system with the mystery red coolant and refill with the proper HOAT coolant. Burp as necessary. See if that solves your overheating problem. If not at least you know the system is clean and has the right coolant in it, you can then move on to looking at possible other causes such as a failed fan clutch.

I'm starting to lean toward this being the next step too

 

[lBasket]

I agree, I think I would be seeing rapid temp fluctuations if there was air in the system (since I’ve had discovered this hwy temp issue, rapid temp changes hasn’t been an issue on the OBD reader)

I originally decided to dilute my redish (not rust) coolant from the PO because when I tested it using my Preston’s gauge, the arrow was pointed all the way off (off the scale, well above the 268 degree boiling temp mark). I’ve been pulling the straight coolant out and mixing it 50/50 with distilled until I got to this point yesterday which I believe should be close to 50/50 in the whole cooling system. Attached picture is the 50/50 mix I’ve been putting into the radiator. When I tested the radiator last night after the last addition of 50/50 and 25 mile hwy drive, I was at the 268 boil mark on the gauge

I’m tempted to go drain all this red coolant, and replace it with the GO5 everyone on here recommends. Hopefully if I don’t get it all out it doesn’t gell up by mixing the two (some posts about that on this forum) Then if it’s not that, maybe the fan clutch?

what is this prestone gauge you're talking about? Also, your pic didn't load

 

[Bowhunter]

So, right now you are running an unknown type of red colored coolant and you have been diluting it with water as well. That's a problem. Next step should be to do the coolant system chemical flush right now. Then fully drain the system with the mystery red coolant and refill with the proper HOAT coolant. Burp as necessary. See if that solves your overheating problem. If not at least you know the system is clean and has the right coolant in it, you can then move on to looking at possible other causes such as a failed fan clutch.

I’ll grab the stuff to do that tonight. For the cleaner, any of them you recommend specifically? And is it something you can typically add to the existing coolant or need to drain coolant and use distilled water for the clean?

 

[Bowhunter]

what is this prestone gauge you're talking about? Also, your pic didn't load

Attaching picture of the dilluted coolant with distilled water. After my dillusions, coolant in rad reads about 268 where it used to be way off the chart pointed up

 

[MikeE024]

What does the gauge on the dash read? My Jeep had a similar issue when I bought it. First thing I would do is a good chemical flush. The kind you leave in there for 6-8 hours before draining it. My 03' Rubicon was taken care of and still had a bunch of crud/rust come out. It's fine after two separate flushes.

When you did the chemical flush, did you use the chemical both times you flushed it, or only the first time? I'm getting ready to do this myself, bought a bottle of blue devil.

I did the same using thermocure. Drain the old coolant and fill the system up with thermocure and distilled water. It will turn black and smell like fish once it’s doing what it’s supposed to do. It works really well and takes multiple flushes to get back to clear water. Then add zerex G05 coolant.

Edit: Drain the block if you can it’s worth it. I believe I used an 8mm square driver and since changed it to a hex.

My engine has been ran a bunch in 4low during AZ summers and more recently has had high intake temps from the turbo (without intercooler). My coolant temps don’t budge over the norm. Make sure you have a good running 195* thermostat in there was well.

 

[Link]

If your system isn't very dirty (yours looks good) skip the coolant flush products. If your system isn't very dirty you are wasting your money. Drain every thing to the best of your ability and refill the entire system with distilled water. A vacuum fill tool is awesome for getting it full without air but not mandatory. Run it for a few days, then drain and refill with distilled water again. Run it for a few more days. Drain again. By now, there should be very little of the old coolant left. Then, refill using a 60/40 mix of GO5. You will have some distilled water still in your system so putting 60/40 in it should end up really close to 50/50. Alternatively, figure out how much coolant your total system holds and pour in 1/2 that much in GO5. Then, top off with distilled water and you are right at 50/50.

 

[MikeE024]

If your system isn't very dirty (yours looks good) skip the coolant flush products. If your system isn't very dirty you are wasting your money. Drain every thing to the best of your ability and refill the entire system with distilled water. A vacuum fill tool is awesome for getting it full without air but not mandatory. Run it for a few days, then drain and refill with distilled water again. Run it for a few more days. Drain again. By now, there should be very little of the old coolant left. Then, refill using a 60/40 mix of GO5. You will have some distilled water still in your system so putting 60/40 in it should end up really close to 50/50. Alternatively, figure out how much coolant your total system holds and pour in 1/2 that much in GO5. Then, top off with distilled water and you are right at 50/50.

The worst part of the process you described is the multiple drain and flushes. Adding thermocure increases your chances of getting max value for your effort.

Many of our systems have aluminum, brass, copper (heater core), and cast iron all in a system with an electrolyte that allows for galvanic corrosion. That’s part of why flushes need to be done.

Thermocure removes the corrosion. It’s not used bc the fluid looks dirty.

I prefer to use it to ensure my cast iron water jackets have potential corrosion build up removed. And, If you have a bit of corrosion impeding flow in the radiator it will eat it and be removed when u drain the system.

If your water turn black then it tells you that you had corrosion in the system. If it doesn’t do anything then at least you know. I’ve done two Jeeps and both turned the solution black as night. Like I said, my system runs pristine. I put Mopar parts in after ensuring corrosion wouldn’t undermine their ability to work properly.

Imo, it doesn’t make sense to go to the effort of flushing multiple times and not do something so simple.

 

[MikeE024]

Additionally, I don’t like air being in the system after changing the coolant and I hate babysitting the radiator cap area and dealing with the mess.

I found this tool to be amazing for burping the system. I squeeze the hoses and air will come out beyond at least 20 minutes longer than I thought would be necessary. I think it took around 45 minutes two years ago and I never needed to fuss with coolant temps again.

Just makes sure you keep it filled and the. Put the stopper in and dump the excess in the reservoir when you are done. I’m a fan.

 

[LONGJP2]

When it stops drawing coolant from the reservoir after several hot/cool cycles then is should be full.

 

[Bowhunter]

I’m going to give the thermocure a try. Drain plug looks to be a little rusty

But I have a follow up question

1. Concerned about removing the block drain plug (for making a less reason, I have a small dog that I don’t want licking coolant as well as if the plug is stuck in there reason) Is this essential or is there an equally good way to drain?

 

[MikeE024]

I’m going to give the thermocure a try. Drain plug looks to be a little rusty

But I have a follow up question

1. Concerned about removing the block drain plug (for making a less reason, I have a small dog that I don’t want licking coolant as well as if the plug is stuck in there reason) Is this essential or is there an equally good way to drain?

View attachment 421578

I would drain from the radiator then drain the block. IIRC there’s about a gallon sitting down in the block. If you don’t crack it open, you could instead drain the coolant from the radiator and then do one flush with water before throwing the thermocure in (that way you get most of the coolant out).

For my first rig, I didn’t drain the block. After flushing the thermocure out with distilled water (multiple rounds), I did one gallon of concentrate to offset the water in the block and then did 50/50 to top it off.

For the second rig, I drained the block and saw loads of rust scale come out. It’s hard for me to not recommend draining the block after seeing what came out.

For both rigs, I drove around with the thermocure about a day (maybe more). I looked for the fluid to turn black and it did both times. I then did flushes after running the engine at temperature so the fluid would cycle through the thermostat.

I had a puppy during the first Jeep drain and the same doggy during the drain on my current Jeep. I didn’t have any issues but I drained from the radiator drain and then lower radiator hose for flushes into a bin when I was impatient. I made a mess but I was mindful and cleaned it all up and sprayed the area down out of paranoia.

I used about 16–18 gallons of distilled water for each but your ocd may vary.

You could use liquid wrench on the drain plug or maybe even crack it after thermocure has worked on the plug.

This is the tool I used. I bought two just in case. It was on tight but cracked off with controlled torque.

I changed the upper and lower hoses both times as well bc they were aged.

Edit: organization

 

[Bowhunter]

I would drain from the radiator then drain the block. IIRC there’s about a gallon sitting down in the block. If you don’t crack it open, you could instead drain the coolant from the radiator and then do one flush with water before throwing the thermocure in (that way you get most of the coolant out).

For my first rig, I didn’t drain the block. After flushing the thermocure out with distilled water (multiple rounds), I did one gallon of concentrate to offset the water in the block and then did 50/50 to top it off.

For the second rig, I drained the block and saw loads of rust scale come out. It’s hard for me to not recommend draining the block after seeing what came out.

For both rigs, I drove around with the thermocure about a day (maybe more). I looked for the fluid to turn black and it did both times. I then did flushes after running the engine at temperature so the fluid would cycle through the thermostat.

I had a puppy during the first Jeep drain and the same doggy during the drain on my current Jeep. I didn’t have any issues but I drained from the radiator drain and then lower radiator hose for flushes into a bin when I was impatient. I made a mess but I was mindful and cleaned it all up and sprayed the area down out of paranoia.

I used about 16–18 gallons of distilled water for each but your ocd may vary.

You could use liquid wrench on the drain plug or maybe even crack it after thermocure has worked on the plug.

This is the tool I used. I bought two just in case. It was on tight but cracked off with controlled torque.

I changed the upper and lower hoses both times as well bc they were aged.

Edit: organization

Thanks for taking the time to break that down, I appreciate it!

If I use thermocure, I would think I’d have to drain the block before putting in the new coolant because if not then I have a gallon of liquid in the block with some thermocure that would stay in the cooling system and I don’t think I should keep the thermocure in long term.

I ordered that tool. Local auto parts store doesn’t carry the thermocure. Any other decent cleaning products or is that really the only one worth using?